1. Field of the Invention
The present invention relates to a battery-operated grease gun, and more particularly to a battery-operated grease gun with an electronic pressure regulator that will allow grease to be discharged in multiple stages at different pressures.
2. Description of Related Art
Battery-operated grease guns make lubricating parts in machines much easier. With reference to FIG. 7, a conventional battery-operated grease gun has a body (60), a pump assembly (not numbered) and a cylindrical lubricant reservoir (61). The body (60) has a grease channel (601), a ball check valve (62) and a discharge spout (63). The grease channel (601) has an inner opening (not numbered) and an outer opening (not numbered). The ball check valve (62) is mounted in the body (60) and communicates with the outer opening in the grease channel (601). The ball check valve (62) has a ball (621), a spring (622) and a threaded plug (623) and is held in place by the threaded plug (623). The discharge spout (63) is attached to the body (60) and communicates with the ball check valve (62).
The pump assembly is mounted in the body (60) and comprises a motor (64) with a drive shaft (641), a three-stage planetary gear assembly (65), a drive disk (66), a drive pin (67), a sliding block (68), a plunger (69) and a drive channel (not numbered) defined in the body (60). The sliding block (68) is slidably mounted in the drive channel and has a transverse cam slot (not numbered). The planetary gear assembly (65) has a sun gear (651) attached to the drive shaft (641) and reduces the speed and increases the torque of the drive shaft (641). The drive disk (66) is coupled to and rotated by the planetary gear assembly (65) and has an eccentric threaded hole (not numbered). The drive pin (67) has a threaded end (not numbered) and a bottom end (not numbered). The threaded end is screwed into the eccentric threaded hole in the drive disk (66), and the bottom end extends out of the eccentric threaded hole and into the transverse cam slot in the sliding block (68) to reciprocally drive the sliding block (68). The plunger (69) has a distal end (not numbered) and a proximal end (not numbered). The distal end is held slidably in the grease channel (601), and the proximal end is attached to the sliding block (68). The cylindrical lubricant reservoir (61) is attached to the body (60) and communicates with the grease channel (601) to supply the lubricant to the grease channel (601).
To discharge the grease, the motor (64) rotates the planetary gear assembly (65) that rotates the drive disk (66). The rotating drive disk (66) and drive pin (67) move the sliding block (68) reciprocally through the drive pin (67). The sliding block (68) simultaneously moves the plunger (69) with a reciprocating motion to pump the grease out through the discharge spout (63). To control the flow rate and flow speed of the grease oil, the threaded plug (623) can be screwed into the body (60) to compress the spring (622). Compression of the spring (622) with the threaded plug (623) applies a greater force on the ball (621), which loads the motor (64) and causes the grease to be discharged at a slower rate and speed.
Consequently, the conventional way to control the flow rate of the grease is tightening the threaded plug (623) to compress the spring (622). However, tightening the threaded plug (623) to control the flow rate is imprecise, at best. Furthermore, the three-stage planetary gear assembly (65) is large and causes the body (60) of the grease gun to be large. Since the sliding block (68) is driven by only one drive disk (66), power transmission between the drive pin (67) and the sliding block (68) only depends on one-side load, the drive disk (66), and is not reliable. One-side load on the sliding block (68) will cause a biasing force that will cause localized friction on the sliding block (68). The sliding block (68) wears unevenly and is not durable.
To overcome the shortcomings, the present invention provides a battery-operated grease gun with an electronic pressure regulator to control the pressure of the discharging grease to mitigate or obviate the aforementioned problems.